I'm planing about recreating inside a garage a small home studio. It's kinda large and inside of it I build two walls so I can setup a closed area to create my studio.

Now two opposite sides have to be 2 meters large, the others two can go up to 4 meters, and this is my concern

Do you have suggestions for what is the minimum required length for the other two opposite sides? I'd like to save as much space as possible. At the same time I don't wanna build something too small to be practical.

Now, since recording studios can have many different purposes, this is mine: I will only record stuff with my master 88 keyboard, I will not record any other live instrument as voice or drums (I don't think it will never be a problem to fit a guitar/bass). I need enough space just for me, my keyboard, my Yamaha HS7, my desk/PC/monitor (no racks), and space to have a good sound decent sound. I do not mind staying in a small place, providing it won't be too much unconfortable or bad for the sound.

Its the parallel walls which could pose a problem (strong resonance). You could try to make them not parallel and the smaller the room, the more its important to dampen it. Bass traps might help as well... Yes, the bigger the better, but if you get it fairly dry its still fine. In a dry small room you can also record audio, you would have to deliver the reverb through headphones for the musician, (its more fun to sing in the church...; - )

There is a site that lets you put in room dimensions (height is often overlooked but crucial) if you really want a well behaved room. I have that site in my favorites somewhere but can't find it sorry. 2 x 4 x 8 is actually a horrible ratio for an audio room by the way. And yes, non-parallel surfaces, including the ceiling are a good start.

I have seen some incredibly effective setups literally in cupboards. Creativity is the key.

Me too ... but only really effective at very low volumes. I like to be able to walk away from my monitors once in a while, especially when working at higher volumes, but in the end you gotta make do with the space available.

Another thing to look out for is the height you set monitors at. Its best not to have them equidistant from the floor & ceiling.

I have seen some incredibly effective setups literally in cupboards. Creativity is the key.

Me too ... but only really effective at very low volumes. I like to be able to walk away from my monitors once in a while, especially when working at higher volumes, but in the end you gotta make do with the space available.

Another thing to look out for is the height you set monitors at. Its best not to have them equidistant from the floor & ceiling.

Oh yeah same here. Ergonomics is a big thing for me but if you're determined you'll find a way to utilise even the most limited space.

Honestly all you need now is a laptop and some headphones. I would say well over half of my stuff is done on a Surface at my local coffee shop.

"I was wondering if you'd like to try Magic Mushrooms"
"Oooh I dont know. Sounds a bit scary"
"It's not scary. You just lose a sense of who you are and all that sh!t"

There are a ton of articles on home studio design, read up quite a bit from the pros before you start building. I know you're looking for specifics on your dimension question, and that's smart to check all that. Just thought I'd share a little on my crappy room, if it helps.

I have a very small studio due to my house's space limitations, it's 11 x 16 x 8H at it's highest point, and the ceiling slopes up for about half the space (the only good thing about this room). Wood floors, wood paneling on one wall, sheetrock on the rest. Needless to say, less than ideal. But I've also produced some award-winning video tracks in there too, so it's not as big a limitation as you might think. After using this studio for almost 20 years here are a few things that work for me...

Near field monitoring at comfortable volumes is your friend. Get a really good pair of NF studio monitors, and then calibrate them as best you can (many monitors have adjustments now) and learn how they respond compared to other speakers. Play well produced music from professionals, and crappy mixes too. Note your thoughts and volumes. I ended up with 3 songs that are a great reference for me on every mix, and over time I've learned my speakers rather well. For me, I think this is one of the most important things; it almost takes the crappy room out of the equation.

The other crucial thing for me is continually checking my mixes on other systems... a friend's house, cars, wherever. I may check a mix occasionally on headphones or buds, after I've done all the other places, but I'm not a fan of that for mixing, it's far too inaccurate... although it can certainly be done, it's much harder, at least for me. But by seeing how your mix translates all across the board is the best test IMHO... after all, it's fairly easy to get a good mix for just one set of speakers. The whole challenge is to produce a mix that sounds great everywhere.

A little bit of treatment goes a long way. I made some small bass traps from rock wool for the corners up near the ceiling. Helps a little. A short carpet runner on the floor near the back wall helps a little too. But don't put carpet on the walls... there are several articles on that. However, after a while I learned how each part of the room sounds.

There's software and a reference mic you can get, can't remember the name, but it will tell you exactly what's wrong with your room, so you can treat it accordingly. I think it also has some design info. I haven't done that though, it's a bit pricey IIRC. Just search, you'll find it.

Don't underestimate how quickly the space gets used up. You never know, what if you join a band and the studio becomes your practice space? Or you get a Hammond, or another synth. Personally, I'd go as large as you can, while keeping in the best proportions you can.

Last, one trick I stumbled on many years ago, is when I've got things roughed in pretty well and have done a little EQ and it's starting to sound good, go out of the room, with the door open, crank your mix up a bit to compensate, and listen to it there. I go about 20' away. It's great to check mix balances, especially for vocals and harmonies. But don't EQ based on that... you'd get all kinds of distortions of EQ from the walls, materials, etc. Mixing with pink noise is interesting too, and sort of does the same thing.

Don't get me wrong, proper Control Room and studio design is very important. But if I had a choice between one or the other, I'd work in a crappy control room, and put my money into a studio space that sounds great... to me, that makes the most difference in the quality of my tracks. Then again, you say you're not doing mics or vocals (at least not yet), so maybe that's not important for you.

From what I've read, a square room isn't ideal. Better to have a rectangular space with the monitors pointing down the longer walls ... so 2x4 would be better (imho).

Hm, that's exactly how i did it... without much thought or consideration. I had my computer desk in a typical bass trap corner before though, and it absolutely sucked... horrible and inconsistent sound.